U.S. patent application number 15/182055 was filed with the patent office on 2017-12-14 for electro-acoustic driver having compliant diaphragm with stiffening element.
The applicant listed for this patent is Bose Corporation. Invention is credited to Brock Jacobites, Nicholas John Joseph, Marek Kawka, Thomas Landemaine, Andrew D. Munro, Prateek Nath, Christopher A. Pare, Adam Sears.
Application Number | 20170359655 15/182055 |
Document ID | / |
Family ID | 60573347 |
Filed Date | 2017-12-14 |
United States Patent
Application |
20170359655 |
Kind Code |
A1 |
Sears; Adam ; et
al. |
December 14, 2017 |
ELECTRO-ACOUSTIC DRIVER HAVING COMPLIANT DIAPHRAGM WITH STIFFENING
ELEMENT
Abstract
An electro-acoustic driver includes a diaphragm formed of a
compliant material, a bobbin configured to hold a winding of an
electrical conductor and a housing having a housing axis that is
substantially coaxial with the bobbin. The diaphragm is fixed to
one end of the housing and has a substantially planar shape when
the diaphragm is at rest. A stiffening element is fixed to an inner
region of a surface of the diaphragm. A motion of the bobbin along
a bobbin axis generates a movement of the inner region of the
diaphragm to thereby generate an acoustic signal that propagates
from the diaphragm.
Inventors: |
Sears; Adam; (Shrewsbury,
MA) ; Pare; Christopher A.; (Franklin, MA) ;
Jacobites; Brock; (Hopkinton, MA) ; Munro; Andrew
D.; (Arlington, MA) ; Landemaine; Thomas;
(Allston, MA) ; Joseph; Nicholas John; (Boston,
MA) ; Kawka; Marek; (Bolton, MA) ; Nath;
Prateek; (Southborough, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bose Corporation |
Framingham |
MA |
US |
|
|
Family ID: |
60573347 |
Appl. No.: |
15/182055 |
Filed: |
June 14, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04R 9/025 20130101;
H04R 9/06 20130101; H04R 7/24 20130101; H04R 7/16 20130101; H04R
31/006 20130101; H04R 7/04 20130101 |
International
Class: |
H04R 7/24 20060101
H04R007/24; H04R 7/16 20060101 H04R007/16; H04R 7/04 20060101
H04R007/04; H04R 9/06 20060101 H04R009/06; H04R 9/02 20060101
H04R009/02 |
Claims
1. An electro-acoustic driver comprising: a diaphragm formed of a
compliant material and having a perimeter, a front surface, a back
surface, an inner region and an outer region between the perimeter
and the inner region, and a substantially planar shape when the
diaphragm is at rest; a bobbin having an inner surface, an outer
surface and a bobbin axis, the bobbin configured to hold a winding
of an electrical conductor on the outer surface; a housing having
an end and a housing axis that is substantially coaxial with the
bobbin axis, the perimeter of the diaphragm being fixed to the end
of the housing; and a stiffening element fixed to one or more of
the front surface and the back surface at the inner region of the
diaphragm, wherein a motion of the bobbin along the bobbin axis
generates a movement of the inner region of the diaphragm to
thereby generate an acoustic signal that propagates from the front
surface of the diaphragm.
2. The electro-acoustic driver of claim 1 wherein the stiffening
element comprises a rigid object disposed inside the bobbin and
secured to the front surface or the back surface of the diaphragm
at the inner region.
3. The electro-acoustic driver of claim 2 wherein the rigid object
is a thin film disc.
4. The electro-acoustic driver of claim 3 wherein the thin film
disc comprises a polyimide film.
5. The electro-acoustic driver of claim 2 further comprising a
bonding agent disposed between a surface of the rigid object and
the front surface or the back surface of the diaphragm.
6. The electro-acoustic driver of claim 1 wherein the stiffening
element is a cured layer of an adhesive.
7. The electro-acoustic driver of claim 1 wherein the bobbin
further comprises a substantially planar surface at an end of the
bobbin, the substantially planar surface being normal to the bobbin
axis and fixed to the back surface of the diaphragm at the inner
region, and wherein the stiffening element comprises the
substantially planar surface of the bobbin.
8. The electro-acoustic driver of claim 7 wherein the substantially
planar surface is fixed directly to the back surface of the
diaphragm.
9. The electro-acoustic driver of claim 7 further comprising a
layer of adhesive to fix the substantially planar surface of the
bobbin to the back surface of the diaphragm at the inner
region.
10. The electro-acoustic driver of claim 1 wherein the bobbin has
an outer diameter and the inner region of the diaphragm has a
diameter that is substantially equal to the outer diameter of the
bobbin.
11. The electro-acoustic driver of claim 10 wherein the outer
region has an annular shape.
12. An electro-acoustic driver, comprising: a housing having a
cylindrical shape, a housing axis and an outer diameter that is
less than about 4.5 mm; a bobbin having a bobbin axis that is
substantially coaxial with the housing axis, the bobbin disposed
inside the housing and configured to move along the bobbin axis; an
acoustic diaphragm secured to the bobbin; and a compliant
suspension surrounding the acoustic diaphragm and secured to the
acoustic diaphragm and the housing.
13. The electro-acoustic driver of claim 12 further comprising a
magnet assembly disposed inside the bobbin.
14. The electro-acoustic driver of claim 12 further comprising a
coil assembly secured to the bobbin.
15. The electro-acoustic driver of claim 12 wherein the acoustic
diaphragm and the compliant suspension are substantially planar
when at rest.
16. The electro-acoustic driver of claim 12 wherein the acoustic
diaphragm and the compliant suspension are formed from a membrane
of a compliant material and wherein the electro-acoustic driver
further comprises a stiffening element fixed to an inner region of
the membrane.
17. The electro-acoustic driver of claim 16 wherein the inner
region is a circular region that is concentric with the compliant
suspension.
18. The electro-acoustic driver of claim 16 wherein the stiffening
element is a cured layer of an adhesive.
19. The electro-acoustic driver of claim 16 wherein the stiffening
element is a rigid object.
20. The electro-acoustic driver of claim 16 wherein the bobbin
includes a substantially planar surface fixed to the inner region
of the membrane.
21. The electro-acoustic driver of claim 12 wherein the outer
diameter of the housing is between about 3.0 mm and 4.5 mm.
22. The electro-acoustic driver of claim 12 wherein the outer
diameter of the housing is between about 3.3 mm and 4.2 mm.
23. The electro-acoustic driver of claim 12 wherein the outer
diameter of the housing is between about 3.6 mm and 3.9 mm.
24. The electro-acoustic driver of claim 13 wherein the magnet
assembly comprises at least one magnet piece and wherein the magnet
piece has a diameter that is between about 1.5 mm and 4.5 mm.
25. The electro-acoustic driver of claim 13 wherein the magnet
assembly comprises at least one magnet piece and wherein the magnet
piece has a diameter that is between about 2.0 mm and 4.0 mm.
26. The electro-acoustic driver of claim 13 wherein the magnet
assembly comprises at least one magnet piece and wherein the magnet
piece has a diameter that is between about 2.5 mm and 3.5 mm.
27. The electro-acoustic driver of claim 12 wherein a ratio of a
radiating area of the driver to a total cross sectional area of the
driver is about 0.7.
28. The electro-acoustic driver of claim 12 wherein a ratio of a
radiating area of the driver to a total cross sectional area of the
driver is between about 0.57 and 0.7.
29. The electro-acoustic driver of claim 12 wherein a ratio of a
radiating area of the driver to a total cross sectional area of the
driver is between about 0.6 and 0.67.
30. The electro-acoustic driver of claim 12 wherein a ratio of a
radiating area of the driver to a total cross sectional area of the
driver is between about 0.62 and 0.65.
31. A diaphragm for an electro-acoustic driver comprising: a
compliant membrane having a perimeter, a front surface, a back
surface, an inner region, an outer region between the perimeter and
the inner region, and a substantially planar shape when the
diaphragm is at rest; and a stiffening element fixed to one of the
front surface and the back surface of the compliant membrane at the
inner region.
32. The diaphragm of claim 31 wherein the stiffening element
comprises a rigid object.
33. The diaphragm of claim 31 wherein the stiffening element is a
cured layer of an adhesive.
Description
BACKGROUND
[0001] This disclosure relates to an electro-acoustic device having
a compliant diaphragm. More particularly, the disclosure relates to
a miniature electro-acoustic driver having a rigid and
substantially planar acoustic diaphragm and a compliant
surround.
SUMMARY
[0002] In one aspect, an electro-acoustic driver includes a
diaphragm, a bobbin, a housing and a stiffening element. The
diaphragm is formed of a compliant material and has a perimeter, a
front surface, a back surface, an inner region and an outer region
between the perimeter and the inner region, and a substantially
planar shape when the diaphragm is at rest. The bobbin has an inner
surface, an outer surface and a bobbin axis. The bobbin is
configured to hold a winding of an electrical conductor on the
outer surface. The housing has an end and a housing axis that is
substantially coaxial with the bobbin axis. The perimeter of the
diaphragm is fixed to the end of the housing. The stiffening
element is fixed to the front surface or the back surface at the
inner region of the diaphragm. A motion of the bobbin along the
bobbin axis generates a movement of the inner region of the
diaphragm to thereby generate an acoustic signal that propagates
from the front surface of the diaphragm.
[0003] Examples may include one or more of the following
features:
[0004] The stiffening element may include a rigid object disposed
inside the bobbin and secured to the front surface or the back
surface of the diaphragm at the inner region. The rigid object may
be a thin film disc. The thin film disc may include a polyimide
film. A bonding agent may be disposed between a surface of the
rigid object and the front surface or the back surface of the
diaphragm.
[0005] The stiffening element may be a cured layer of an
adhesive.
[0006] The bobbin may further include a substantially planar
surface at an end of the bobbin such that the substantially planar
surface is normal to the bobbin axis and is fixed to the back
surface of the diaphragm at the inner region, wherein the
stiffening element includes the substantially planar surface of the
bobbin. The substantially planar surface may be fixed directly to
the back surface of the diaphragm. Alternatively, a layer of
adhesive fixes the substantially planar surface of the bobbin to
the back surface of the diaphragm at the inner region.
[0007] The inner region of the diaphragm may have a diameter that
is substantially equal to an outer diameter of the bobbin and the
outer region may have an annular shape.
[0008] In accordance with another aspect, an electro-acoustic
driver includes a housing, a bobbin, an acoustic diaphragm and a
compliant suspension. The housing has a cylindrical shape, a
housing axis and an outer diameter that is less than about 4.5 mm.
The bobbin has a bobbin axis that is substantially coaxial with the
housing axis. The bobbin is disposed inside the housing and is
configured to move along the bobbin axis. The acoustic diaphragm is
secured to the bobbin and the compliant suspension surrounds the
acoustic diaphragm and is secured to the acoustic diaphragm and the
housing.
[0009] Examples may include one or more of the following
features:
[0010] The electro-acoustic driver may further include a magnet
assembly disposed inside the bobbin.
[0011] The electro-acoustic driver may further include a coil
assembly secured to the bobbin.
[0012] The acoustic diaphragm and the compliant suspension may be
substantially planar when at rest.
[0013] The acoustic diaphragm and the compliant suspension may be
formed from a membrane of a compliant material and the
electro-acoustic driver may further include a stiffening element
fixed to an inner region of the membrane. The inner region may be a
circular region that is concentric with the compliant suspension.
The stiffening element may be a cured layer of an adhesive or a
rigid object. The bobbin may include a substantially planar surface
fixed to the inner region of the membrane.
[0014] The outer diameter of the housing may be between about 3.0
mm and 4.5 mm, between about 3.3 mm and 4.2 mm, or between about
3.6 mm and 3.9 mm.
[0015] The magnet assembly may include at least one magnet piece
and the magnet piece may have a diameter that is between about 1.5
mm and 4.5 mm, between about 2.0 mm and 4.0 mm, or between about
2.5 mm and 3.5 mm.
[0016] A ratio of a radiating area of the driver to a total cross
sectional area of the driver may have a value of about 0.7, a value
between about 0.57 and 0.7, a value between about 0.6 and 0.67 or a
value between about 0.62 and 0.65.
[0017] In accordance with another aspect, a diaphragm for an
electro-acoustic driver includes a compliant membrane and a
stiffening element. The compliant membrane has a perimeter, a front
surface, a back surface, an inner region, an outer region between
the perimeter and the inner region, and a substantially planar
shape when the diaphragm is at rest. The stiffening element is
fixed to one of the front surface and the back surface of the
compliant membrane at the inner region.
[0018] Examples may include one or more of the following
features:
[0019] The stiffening element may include a rigid object.
[0020] The stiffening element may be a cured layer of an
adhesive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and further advantages of examples of the present
inventive concepts may be better understood by referring to the
following description in conjunction with the accompanying
drawings, in which like numerals indicate like structural elements
and features in various figures. The drawings are not necessarily
to scale, emphasis instead being placed upon illustrating the
principles of features and implementations.
[0022] FIG. 1A, FIG. 1B and FIG. 1C are a perspective view, a
cutaway view and an exploded cutaway view, respectively, of an
electro-acoustic driver.
[0023] FIG. 2 is an illustration of the diaphragm of FIGS. 1A to
1C.
[0024] FIG. 3 is a cross-sectional side view of the housing, bobbin
and coil assembly of FIGS. 1A to 1C according to an example in
which an inner region of the diaphragm is stiffened by an
adhesive.
[0025] FIG. 4 is an alternative example in which a rigid object is
used to stiffen the inner region of the diaphragm
[0026] FIG. 5 is another alternative example in which a bobbin
includes a planar surface to stiffen the inner region of the
diaphragm.
DETAILED DESCRIPTION
[0027] Modern in-ear headphones, or earbuds, typically include
microspeakers. The microspeaker may include a coil wound on a
bobbin that is attached to an acoustic diaphragm. Motion of the
diaphragm due to an electrical signal provided to the coil results
in generation of an acoustic signal that is responsive to the
electrical signal. The microspeaker may include a housing, such as
a sleeve or tube, which encloses the bobbin and coil, and a
magnetic structure. As the size of the earbud decreases, it becomes
increasingly difficult to fabricate the acoustic diaphragm and
surrounding suspension at one end of the bobbin and housing.
[0028] FIG. 1A, FIG. 1B and FIG. 1C are a perspective view, a
cutaway perspective view and an exploded cutaway view,
respectively, of an example of an electro-acoustic driver 10 (e.g.,
a microspeaker) that can be used in a miniature earbud. The
microspeaker 10 includes a cylindrical housing 12 having an opening
at both ends. Inside the housing 12 is a bobbin 14 that is
nominally cylindrical in shape and open at both ends. In some
examples, the housing 12 is made of stainless steel and the bobbin
14 is made of a polyimide (e.g., KAPTON.RTM.) or polyethylene
terephthalate (PET) (e.g., MYLAR.RTM.). The housing 12 and bobbin
14 are secured at one of their open ends to a diaphragm, or
membrane, 16 formed of a compliant material such as an elastomer. A
coil assembly 18 is wound onto an outside surface of the bobbin 14.
The coil assembly 18 includes a winding of an electrical conductor
and may include a structure to hold the winding is a desired shape
and/or to secure the winding on the outer surface of the bobbin 14.
A magnet assembly 20 is secured to a platform 22 at an end of the
housing 12 that is opposite to the diaphragm 16. The magnet
assembly 20 includes two magnet pieces 20A and 20B that can be, for
example neodymium magnets, and an intervening coin 20C. The magnet
assembly 20 extends along a housing axis 24 (i.e., a cylinder axis)
and into an open region inside the bobbin 14. The axis of the
bobbin 14 is substantially co-axial with the housing axis 24.
[0029] The electro-acoustic driver 10 may be miniaturized such that
the outer diameter .phi..sub.H of the housing and the diameter
.phi..sub.D of the diaphragm 16 are less than about 4.7 mm. The
small dimensions present various fabrication problems, including
how to provide a small acoustic diaphragm supported by a compliant
surround.
[0030] In some examples, the housing 12 has an outside diameter
.phi..sub.H that is less than about 8 mm. In some examples, the
housing 12 has an outside diameter .phi..sub.H that is less than
about 4.5 mm. In other examples, the housing 12 has an outside
diameter .phi..sub.H that is between about 3.0 mm and 4.5 mm. In
other examples, the housing 12 has an outside diameter .phi..sub.H
that is between about 3.3 mm and 4.2 mm. In other examples, the
housing 12 has an outside diameter .phi..sub.H that is between
about 3.6 mm and 3.9 mm. In some examples, the magnet pieces 20
have a diameter .phi..sub.M that is between about 1.5 mm and 4.5
mm. In other examples, the magnet pieces 20 have a diameter
.phi..sub.M that is between about 2.0 mm and 4.0 mm. In other
examples, the magnet pieces 20 have a diameter .phi..sub.M that is
between about 2.5 mm and 3.5 mm. The radiating area is
approximately equal to the area of an inner (central) region of the
diaphragm 16 that is stiffened in any one of a variety of ways,
including those described in detail below. In some examples, a
ratio of the radiating area to the total cross sectional area of
the driver 10 is about 0.7. In some examples, a ratio of the
radiating area to the total cross sectional area of the driver 10
is between 0.57 and 0.7. In some examples, a ratio of the radiating
area to the total cross sectional area of the driver 10 is between
0.6 and 0.67. In some examples, a ration of the radiating area to
the total cross sectional area of the driver 10 is between 0.62 and
0.65.
[0031] Referring also to FIG. 2, the diaphragm 16 is shown in
isolation with its thickness t exaggerated to simplify
identification of various features. The diaphragm 16 may be formed
of an elastomeric material such as a volume of liquid silicone
rubber that is cured to provide the desired thickness t and to
adhere to an end of the bobbin 14 and an end of the housing 12. The
diaphragm 16 has a perimeter, i.e., the circumferential outer edge
at a radius Ro, a front surface 32 and a back surface 34. The
diaphragm 16 includes an inner region inside the dashed circular
line 36 of radius Ri and an outer region defined by an annular
shape that extends from the dashed circular line 36 to the
perimeter. The smaller radius Ri is approximately equal to the
outer diameter of the cylindrical bobbin 14 and the larger radius
Ro is approximately equal to the outer diameter of the housing 12.
By way of non-limiting examples, the diaphragm thickness t can be a
few tens of microns to more than 100 .mu.m and the diameter Ro may
be less than 4.7 mm.
[0032] The bobbin 14 moves substantially along its axis, and the
housing axis 24, in response to an electrical current conducted
through the winding of the coil assembly 18. This motion causes the
inner region of the diaphragm 16 to move axially and displace air
to thereby generate an acoustic signal.
[0033] The diaphragm 16 has a substantially planar shape when at
rest, that is, when no electrical signal is applied to the winding
of the coil assembly 18 to generate sound. When the microspeaker 10
is driven by an electrical signal to cause a motion of the bobbin
14 along the housing axis 24, the compliant nature of the diaphragm
16 results in its deformation. The inner region of the diaphragm 16
acts as an acoustic diaphragm that is used to generate the acoustic
signal; however, due to the low value of Young's modulus for the
diaphragm 16, the inner region can behave similar to a drum head.
In particular, the inner region can exhibit unwanted structural
resonances with the operating frequency band of the driver 10 and
can result in a reduction in driver efficiency.
[0034] In various examples described below, the inner region of the
diaphragm 16 is stiffened, or made rigid, by a stiffening element
to substantially reduce or eliminate unwanted resonances during
operation. The outer region of the diaphragm 16 is a compliant
suspension that surrounds the stiffened inner region. In one
example, the stiffening element is a rigid layer of material that
is secured to the back surface 34 of the diaphragm 16 over the
inner region and which is also secured to the adjacent portion of
the inner surface of the bobbin 14. Alternatively, the stiffening
element is a rigid object that is secured to the back surface 34 of
the diaphragm 16 within the inner region. The object may be a
standalone structure (e.g., a solid disc) or the object may be a
structural feature of the bobbin. As a result of the stiffening of
the inner region, unwanted resonance frequencies are shifted out of
the operating bandwidth of the electro-acoustic driver 10 and/or
the displacement of the diaphragm 16 at these resonance frequencies
is substantially reduced. Consequently, a smoother acoustical
frequency response can be achieved. In addition, stiffening of the
inner region has an additional benefit of increasing the effective
piston area of the electro-acoustic driver to thereby increase the
sound pressure output for a particular bobbin displacement
magnitude.
[0035] FIG. 3 shows a cross-sectional side view of the housing 12,
bobbin 14 and coil assembly 18 according to one example in which
the inner region of the diaphragm 16 is stiffened. A small quantity
of adhesive is dispensed into the "cup-shaped" structure defined by
the bobbin 14 and diaphragm 16 to partially fill the cup. An
adequate volume of adhesive is used to ensure that the inner region
of the diaphragm 16 is fully covered by the adhesive layer. The
adhesive is then cured to form a rigid layer 40 that adheres to a
portion of the inner surface 42 of the bobbin 14 and the back
surface 34 (see FIG. 2) of the diaphragm 16. A meniscus 44 may form
along the inner wall and improve adhesion to the bobbin 14.
[0036] FIG. 4 shows an alternative example in which a rigid object
50 (e.g., disc) is used to stiffen the inner region of the
diaphragm 16. The disc 50 may be a high strength thermoplastic thin
film such as a polyetherimide (e.g., ULTEM.RTM.). The disc 50 has a
diameter that is less than the inner diameter of the bobbin 14 to
enable the disc 50 to be inserted into the bobbin 14; however, the
difference in the diameters is kept small to maximize contact with
the inner region of the diaphragm 16. A thin layer of a bonding
agent, or adhesive, may be used to bond the disc 50 to the inner
region of the diaphragm 16. The bonding agent or adhesive may also
be used to bond to the inner cylindrical surface of the bobbin 14.
Alternatively, the disc 50 may be placed on top of an uncured layer
of an elastomeric material (e.g., liquid silicone rubber) used to
create the diaphragm 16. Subsequent curing of the elastomeric layer
results in a bond of the diaphragm 16 directly to the disc 50 and
the end of the bobbin 14.
[0037] FIG. 5 shows another alternative example in which a bobbin
60 contains structure that is used to stiffen the inner region. The
bobbin 60 has a cylindrical portion 60A similar to the bobbin 14 of
FIG. 3 and FIG. 4; however, the bobbin 60 also includes an end
surface 60B at one end. The end surface 60B may be integrated with
the cylindrical portion 60A as a single body. In an alternative
configuration, the end surface 60B may be formed independently and
then secured to the end of the cylindrical portion 60A. The end
surface 60B may be fixed to the back surface 34 (see FIG. 2) of the
diaphragm 16 along the inner region using a bonding agent or
adhesive. Alternatively, the end surface 60B may be disposed within
an uncured layer of an elastomeric material used to create the
diaphragm 16 so that subsequent curing of the elastomeric material
causes the diaphragm 16 to adhere to the surface 60B.
[0038] A number of implementations have been described.
Nevertheless, it will be understood that the foregoing description
is intended to illustrate, and not to limit, the scope of the
inventive concepts which are defined by the scope of the claims.
Other examples are within the scope of the following claims.
* * * * *